1. Field of the Invention
The present invention relates to a cold rolling system having a tandem structure comprising a plurality of rolling mills each having a powered turks-head roll having driving rolls vertically disposed and free rolls laterally disposed and a non-powered turks-head roll. The present invention also relates to a cold rolling method using the above system.
2. Description of the Background Art
Cold drawing has been employed as means for forming a rail or the like which is uniform in the longitudinal direction thereof. Cold drawing requires a base material having a relatively large cross-sectional area to obtain a desired deformed shape. This increases the total processing rate and often causes a rapture of a material due to insufficient strength thereof or an unstable pressure exerted on that part of the material to be deformed, or cracking or abnormal wear of a die due to insufficient strength thereof. Thus, process annealing is necessary to obtain a desired final shape. Also, in order to prevent wear and seizure of a drawing die due to high sliding friction created by a high bearing pressure between the base material and the die, a chemical solid lubricating coating such as a zinc stearate coating must be provided on surfaces of the base material. This requires a pickling process and a chemical conversion coating process, which may adversely affect the environment. Additionally, the conventional method includes the processes of annealing, pickling and chemical conversion coating and thus needs long lead time, increasing running and equipment costs. Moreover, in conventional drawing, a bar material is usually used, so that the material loss due to the disposal of pointed parts amounts to 10 to 30%. Also, a bar material tends to have a bend at end parts thereof and it takes time to straighten or adjust the bends.
The present invention has been made in view of the drawbacks of the prior arts and it is, therefore, an object of the present invention to provide a cold rolling system and a cold rolling method which can prevent a rapture of a workpiece due to plastic deformation under triaxial compression, which is a feature of cold rolling. The present invention also provides a cold rolling system and a cold rolling method which utilizes mutual sliding between rolls of a very small diameter and a workpiece to eliminate the processes of annealing, pickling and chemical conversion coating and accomplish cost reduction and energy saving. Another object of the present invention to provide a cold rolling system and a cold rolling method which can reduce material loss to 5% or lower and which can decrease dimensional variation among rolled workpieces (within 0.05 mm or lower) and improve straightness of a rolled workpiece including end parts thereof after cutting (final precision of 0.1 mm). Yet another object of the present invention is to provide a cold rolling system and a cold rolling method which can reduce lead time necessary to process a base material before it is introduced into the rolling line and thus can reduce the running and equipment costs.